Abstract Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. This arrhythmia represents a major public health problem as it is associated with several adverse cardiovascular outcomes. Recently, psychological stress has been identified as important risk factor for AF development and interventions aimed at reducing psychological stress could help reduce the burden of this common arrhythmia. However, the mechanisms that link psychological stress with AF have yet to be fully elucidated. Transient changes in left atrial size and pressure during stress may signal increased risk of AF onset, and over time possibly lead to fixed structural changes which predispose to arrhythmia. Therefore, the identification of dynamic changes in left atrial abnormalities on the 12-lead electrocardiogram during stress will allow for the better characterization of at risk populations for stress-induced AF as it will help identify those who are likely to develop the arrhythmia. We hypothesized that acute psychological stress is able to alter left atrial structure and function as detected by left atrial abnormalities on the routine 12-lead electrocardiogram. The preliminary data showed that P-wave terminal force in lead V1 (PTFV1), a commonly reported left atrial abnormality associated with increased left atrial pressure and size, becomes more negative with acute psychological stress. This suggests that acute psychological stress is associated with adverse changes in left atrial pressure and size. To further characterize the association between acute mental stress and left atrial abnormalities, we will examine the change in PTFV1 during acute mental stress on a well-characterized cohort of 1,000 patients with stable coronary artery disease. Aim 1 will compare the mean PTFV1 in patients at rest, during stress, and at recovery. In Aim 2, we will compare mean PTFV1 in patients at the three time periods by participants who experience mental stress-induced myocardial ischemia (MSIMI). Patients who experience MSIMI possibly have impaired left ventricular function that passively increases left atrial pressure and results in the abnormal substrate for AF to propagate. Aim 3 will determine if changes in PTFV1 during acute mental stress are associated with adverse cardiac events in this cohort after two years of follow-up. The goal of this study is to further evaluate left atrial abnormalities as a risk marker for AF during acute mental stress on a well-characterized cohort of patients with stable coronary artery disease. The proposed analyses will provide plausible evidence to link psychological stress with AF by using an experimental approach to study the effects of mental stress on atrial electrophysiology. Additionally, this research will improve our understanding of the role acute mental stress plays in the development of atrial arrhythmias by identifying those who are likely to develop adverse atrial remodeling and improve our understanding of AF susceptibility.